This invention relates to a slot hyperfrequency thin antenna.
2. Discussion of the Background
Flat antennas with radiant slots have been produced in an industrial environment based on a feed structure for waveguides. These embodiments exhibit undeniable qualities at the level of radio performances. On the other hand, the difficulty in constructing the mechanical embodiment leads to a high production cost. Prior attempts to reduce cost have degraded the performance (reduction of the frequency band, . . . ) and decreased the availability of complex functions if the same technology is used.
It is possible to produce flat antennas with a low production cost. For this purpose, the microstrip technology is used in which the radiant elements are formed by discontinuities of the strip: they are designated by the name of radiant patches. The embodiment is simple since it is possible to produce a radiant surface directly by photoengraving. On the other hand, the performance is mediocre compared with the performance of waveguides: significant losses, parasitic radiation of the feeders, etc.
Another technology exists in which it is possible to reduce cost by using photoengraving processes having striplines. In this case, the radiant element is a slot photoengraved in a metal plane and excited by a line according to the process indicated by FIG. 1 (proposed by R. M. Barret and M. H. Barnes in 1951: "Survey of design techniques for flat profiles microwave antennas and arrays, " P. S. Hall and J. R. James, The Radio and Electronic Engineer, Vol. 48 no. 11 pp. 545-565, November 1978, and: "Microwave printed circuits, " R. M. Barret and M. H. Barnes, Radio and TV News, Vol. 46, 1951, p. 16). The modeling and the characterization of this type of radiant element have been performed successively by A. A. Oliner in 1954 ("The radiation conductance of a series slot in strip transmission line, " A. A. Oliner, IRE National Convention Record, 2, Part 8, pp. 89-90 (1954)), R. W. Breithaupt in 1968 ("Conductance data for offset series slots in stripline," R. W. Breithaupt, IEEE Trans-on Microwave Theory and Technique, November 1968, p. 969) and F. S. Rao and B. N. Das in 1978 ("Impedance of off-centered stripline fed series slot, " J. S. Rao and B. N. Das, IEEE Trans. on Antennas and Propagation AP26, November 1978, no. 6, p. 893). As first approximation, the equivalent diagram ordinarily accepted is that of FIG. 2, described below.
An antenna fed by guides whose one end is short-circuited at about one quarter of a wavelength from the end of the core of the strip and whose other end is open on a free half-space by flaring in the shape of a trumpet (see FIG. 6) is further known ("New structures of high-output plane antennas with striplines and suspended striplines," E. Ramos, Radar Symposium, Versailles, May 1984, and: "A plane antenna with lines on suspended substrate for applications of 12 GHz satellite reception," E. Ramos, Acta Electronica, Journal of LEP/Philips, Vol. 27, no. 1/2 1985, pp. 77-83). This arrangement leads to a significant thickness for the entire structure; actually, a section for filtering evanescent modes (generated by the free end of the core of the strip) toward the radiant opening is to be added to the quarter-wave section, already mentioned.